The field of the invention relates generally to an internal combustion engine and, more particularly, to a system and method for cooling a turbocharged engine.
Internal combustion engines such as, but not limited to, turbocharged diesel engines as utilized with locomotives, require cooling systems to limit the temperatures of various engine components. Such engines are designed with water jackets and/or internal cooling passages for the circulation of a coolant to remove heat energy from the engine components, such as, but not limited to, the engine block and cylinder heads. Lubricating oil is circulated throughout the engine to reduce friction between moving parts and to remove heat from components such as the pistons and bearings. The lubricating oil must be cooled to maintain its lubricity and to extend the interval between oil changes.
Some internal combustion engines utilize turbochargers to increase engine power output by compressing the intake combustion air to a higher density. Such compression results in the heating of the combustion air, which must then be cooled prior to entering the combustion chamber to enable the engine to have high volumetric efficiency and low emissions of exhaust pollutants. For mobile applications such as, but not limited to, locomotives, it is known to use a pumped cooling medium such as water to transport heat to finned radiator tubes. The radiator tubes then transfer the heat to the ambient air, often using forced convection provided by a fan. This may be accomplished using a two stage intercooler for conditioning the combustion air entering the engine. A first coolant loop may include a first stage intercooler and a second coolant loop may include a second stage intercooler. This two stage system provides a level of control for maintaining the engine, lubricating oil and combustion air temperatures within respective limits without excessive fan cycling.
Means for lowering manifold air temperature (MAT) have been incorporated in turbocharged piston engine powered vehicles for many decades. Lowering MAT can increase the power available from a given size engine and/or increase the durability of the engine at very high power loads by limiting the temperatures to which components, such as aluminum pistons, are exposed. For light weight vehicles such as piston powered military aircraft and racing automobiles, the need is usually for a large reduction in MAT for a short period of time. For such applications it has been feasible to carry a small amount of water that is injected into the hot intake air when needed. The injected water changes to steam due to the high temperature, thereby absorbing heat and lowering the intake charge temperature. For heavy mobile vehicles such as, but not limited to, turbocharged diesel powered locomotives, which are designed to produce a maximum power output for an indefinite amount of time, it originally sufficed to use water based coolant circuits to transport the heat from an intercooler to a fan cooled radiator, with the coolant from the radiator used for both engine and intercooler alike.
Though internal combustion engines are used in locomotives, these engines are also used in a vast array of other applications where a prime mover is used, such as but not limited to off-highway vehicles, marine vessels, stationary power plants, agricultural vehicles, and transportation vehicles. Further reductions in NOx emissions are being required worldwide when prime movers are operated. In the case of stationary power plants and marine vessels utilizing diesel engines, it is still possible in many cases to meet reduced NOx limits with water based cooling systems that exchange heat to the environment using river, lake, or ocean water that rarely exceeds 26.67 degrees Celsius (80.01 degrees Fahrenheit).
However, the approach used with stationary power plants and marine vessels is not practical for a locomotive due to the need to haul the supply of water along with the train. Towards this end, to eliminate a need for a significant amount of coolant, locomotive and/or train operators and owners would benefit from having a cooling system that does not require a coolant based intercooler and/or intermediate ducts.